Plant root architecture is essential for its functions in water and nutrient uptake, anchorage and interactions with microbes in the soil.
Studies in Arabidopsis have greatly advanced our knowledge on mechanisms controlling root development (Potters G et al., (2007) Trends Plant Sci 12(3):98-105; Peret B, et al. (2009) Trends Plant Sci 14(7):399-408; Lavenus J, et al. (2013) Trends Plant Sci 18(8):450-458); however, similar studies in cereals are relatively scarce (Coudert Y et al., (2010) Trends Plant Sci 15(4):219-226). Unlike Arabidopsis which has a primary root that iteratively branches to generate several orders of lateral roots, the cereals have several types of branched roots including shoot-born crown roots and root-borne lateral roots. Approximately 675 quantitative trait loci (QTLs) control 29 root parameters in rice (Courtois B, et al. (2009) Rice 2(2-3):115-128). Several homologous genes that play similar roles regulating root formation between Arabidopsis and cereals have been identified; however, distinct hormonal and developmental pathways are also found to be involved in root formation in cereals (Orman-Ligeza B, et al. (2013) Trends Plant Sci 18(8):459-467). In Arabidopsis, six classical hormones control primary root growth by targeting cells in distinct tissues (Ubeda-Tomas S et al., (2012) Trends Plant Sci 17(6):326-331). Among these hormones, auxin is shown to act as a common integrator to many endogenous and environmental signals regulating lateral root development in both dicots and monocots (Ubeda-Tomas S et al., supra; Laurie S et al., J Exp Bot 54(383):739-747). In Arabidopsis, the universal stress hormone abscisic acid (ABA) stimulates main root elongation in response to drought and osmotic stresses; however, ABA and auxin signals act antagonistically during lateral root initiation, with ABA as a repressing while auxin a promoting agent (De Smet I et al., (2006) Trends Plant Sci 11(9):434-439).
LEA proteins are a set of proteins highly accumulated at the onset of seed desiccation and in response to water deficit in plant vegetative tissues (Dure L (1981) Biochemistry 20:4162-4168; Dure L (1992) Control of Plant Gene Expression. CRC Press, Boca Raton, Fla., pp. 325-335). LEA proteins have been classified into six groups based on conservation in amino acid sequence domains and expression patterns (Dure L, 3rd (1993) Plant J 3(3):363-369; Wise M J (2003) BMC Bioinformatics 4:52) HVA1 is a group 3 LEA (LEA3) protein specifically expressed in barley aleurone layers and embryos during late seed development undergoing desiccation (Jefferson R A (1987) Plant Mol Biol Rep 5:387-405). HVA1 contains an 11-amino acid consensus motif which is repeated 9 times, forming an α-helical dimmer suitable for accommodating positively and negatively charged ions, thus has been proposed to function as an ion sequester (Liang Y & Harris J M (2005) Am J Bot 92(10):1675-1683). Functions of HVA1 in protection against environmental stresses have been reported (Hong B et al., (1992) Plant Mol Biol 18:663-674; Sutton F et al., Plant Physiol 99(1):338-340). However, no one reports HVA1's function on promoting root growth of plants.